Compressed Air Best Practices - May 2008 - (Page 27)

Compressed Air Industry AUTOMOTIVE ASSEMBLY | 05/08 | Obviously, when the presence of oil is to be avoided, the non-lubricated type would inherently be the most reliable from an “oil carryover” standpoint. This design has historically been a smaller reciprocating compressor (25 hp and smaller), usually air cooled with very limited duty cycle, often 1,000–1,500 hours between overhauls. Centrifugal compressors are “oil-free type” usually with a lubricated “bull gear type” drive. The preferred source of starting air is non-lubricated since oil getting into the centrifugal compressor is not only an inconvenience, but unchecked can lead to premature failure. In reality, the starting air is not often run to the compressor. Stored bottles of nitrogen can be a proper supply of inert, clean, dry gas used to supply starting air. It can be stored at very high pressure and regulated to lower pressure flow which will allow the proper volume of air to be stored in a smaller area — that is, if you know the volume. Nitrogen as a start up gas has several drawbacks: p p III. Common problems with a centrifugal compressor starting air system: p Used for another process — not available when needed. The average centrifugal in a multi-unit installation probably only needs starting air once every three years, or less, but at that time it is very critical. Often during the long unused periods of time, other users “temporarily” tap into this starting air supply “because it’s there!” When starting air is called for these other users will also be on, not leaving enough to start the compressor. p Air is needed — the start up compressor is not in condition to run • • Used for various other services — not maintained Sits for 3 years or more — becomes somewhat forgotten p Starting air compressor runs OK — can’t handle the load • • • How much (cfm) did you size for? Did it used to do the job when new? What has happened? Can the air requirement change? Relatively expensive Often is “borrowed” for another use Small leaks may be undetected — during the long time between uses they may not have sufficient volume to do the job Undersized for the job either initially or because of a change in situation — i.e., leaks on valves, control lines, seals, etc. p p www.airbestpractices.com 27 http://www.ultra-air.com http://www.ultra-air.com http://www.ultra-air.comcsssss http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - May 2008

Compressed Air Best Practices - May 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month Pneumatics Real World Best Practices Delta Industries: Doing What is Right for Customers Delta Industries: Six Truths You Need to Know about Really Putting the Customer First Power Supply Industries Resources for Energy Engineers Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - May 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.